In many processes for copying or duplicating an image or a reversal of an image from one photographic element onto another photographic element, it is often desirable to bring the elements into close contact with one another and expose through the "original" element already having an image thereon to expose the other element. Such contact printing or exposure is often used for high-contrast graphic arts products. This technique may be used for example, to expose through a photographic element having a high-contrast half-tone original onto a lithographic printing plate or to duplicate or make a reversal image by exposing through such a photographic element onto another.
A common technique for bringing the elements into close contact with one another is to juxtapose the elements and draw a vacuum from between them. This is often accomplished with a device known as a vacuum frame. Vacuum frames are widely used in the photographic art and especially in the graphic arts for this purpose.
When smooth surfaced elements are brought into such vacuum contact, however, the time required to evacuate from between the elements and obtain a substantially uniform and complete contact between them becomes exceedingly high. Moreover, even after long periods of time, uniform and complete contact might not be achieved. For this reason, matte particles are often incorporated in the outermost layer of at least one of the elements to provide for efficient evacuation (also known as vacuum draw-down) from between the elements. Matte particles are also useful in preventing the formation of Newton rings that can occur during contact exposure.
The binder of previous matte layers used in element subjected to vacuum draw-down, which is usually gelatin, is generally coated at a level so that a large part of each of the matte particles in the layer resides below the surface of the layer. This inhibits the efficiency of the matte particle at providing the surface of the element with the roughness necessary to achieve the desired vacuum draw-down efficiency. Often, large quantities or particle diameters or both must be used in order to achieve the desired draw-down.